Ordinarily, a vehicle power transmission apparatus has an input member, connected to an engine and transmission, an output member, selectively connected to selectively driven wheels (e.g. front wheels), and clutch members connected to the output member. The power can be transmitted by pressure-contacting a plurality of driving clutch plates, mounted on the input member, and a plurality of driven clutch plates, mounted on a clutch member, and can be cut off by releasing them.
As shown in FIG. 5, a prior art driving clutch plate 101 used in a power transmitting apparatus has a substantially annular configuration. The clutch plate 101 is formed with a plurality of projections 101a which project radially outward from the periphery of the annular body at an equidistant to each other. The driving clutch plate 101 usually has, as shown in FIG. 6, a linear projected wall surface “a” forming an upstanding surface of the projections 101a. The wall surface “a” is adapted to be engaged by a clutch housing 102. Also, the clutch plate 101 has a peripheral surface “b” on the substantially annular body. A connecting surface “c”, having an arcuate configuration of a predetermined curvature, connects the projected wall surface “a” and the peripheral surface “b”.
However since the projected wall surface “a” and the peripheral surface “b” are connected by a connecting surface “c”, without any undercut, a large clearance “CL” exists between the housing 102 and the peripheral surface “b”. This large clearance “CL” is required in order to avoid interference between the housing 102 and the driving clutch plate when the driving clutch plate is assembled onto the clutch housing 102. Accordingly, the substantially linear projected wall surface “a” of the driving clutch plate intimately contacts the clutch housing 102. Thus, the presence of the large clearance “CL” causes an increase in radial size which is a problem in prior art power transmitting apparatus.
On the contrary, it is possible to reduce the clearance “CL” and avoid the interference between the housing and the driving clutch plate, if the radius of curvature of the connecting surface “c” is reduced (i.e. the curvature is enlarged). However the reduction of the radius of curvature of the connecting surface “c” causes stress concentration in the connecting surface “c” and thus a reduction of strength of the driving clutch plate. Accordingly, it is impossible in the prior art power transmission apparatus to simultaneously achieve size reduction and improve the strength of the driving clutch plate.